The largest ever inquiry into the abuse of children at residential homes in the UK will examine the soul of society, a lawyer has said.

Decades of physical, sexual and emotional suffering were inflicted upon the most vulnerable by the church, the state and voluntary organisations, it was alleged today.

More than 300 victims are set to testify to the investigation, which is expected to last 18 months.

Christine Smith QC, the inquiry's senior counsel, told Sir Anthony Hart, a retired Crown court judge presiding over the hearings, that they would give voice to those who felt let down by the system between 1922, the foundation of the Northern Ireland state, and 1995. She said it would essentially examine the soul of Northern Ireland's society.

"There can be no keener revelation of a society's soul than the way in which it treats its children," she said.

The hearing got under way in Banbridge, Co Down, where scores of victims and their families packed the public gallery to hear Ms Smith outline harrowing details of abuse which carried on largely unchecked for more than seven decades.

It involved homes in Belfast, Londonderry and Kircubbin in Co Down as well as the notorious Kincora boys' home in east Belfast where details of alleged abuse of young children first emerged decades ago.

The aim of the investigation is to establish if there were "systemic failings by institutions or the state in their duties towards those children in their care".

It was created in response to a campaign for justice by victims, which became increasingly urgent in 2009 following the findings of a similar investigation in the Republic of Ireland which uncovered evidence of endemic abuse.

Most complaints relate to Catholic homes for children looked after between the end of the Second World War and the end of the 1970s. They were commonly orphans, others came from families deemed unfit to care for them.

Ms Smith said many victims had waited years for the start of the inquiry, for the opportunity to give their accounts of what happened.

"The core of its work is a very human story, a story of how society treated the must vulnerable of its citizens, its children. Such stories are sadly not unique to Northern Ireland," she added.

.For many it will be the first time they state in public what happened to them.

The senior lawyer said: "For many, giving evidence over the coming months will be a very difficult experience.

"This inquiry, both through the work of the acknowledgment forum and these hearings, is giving a voice to those who feel the system let them down."

Around 97,000 pages of evidence have been submitted.

The allegations included:

:: Sexual attacks by staff, adults or older children.

:: Physical assaults by staff with implements.

:: Bullying by older children.

:: Denigration of their families or separation from brothers or sisters.

Sir Anthony said he hoped every person who gave evidence to the public hearings or only spoke during the private and confidential part of the inquiry would have the satisfaction of knowing that their experiences were at last being listened to and investigated.

"I say at last being listened to because one of the things that we have heard again and again is that when complaints about abuse were made to people in authority, all too often their response was to ignore, or not to believe, what they were being told."

He said the investigation allowed everybody involved in the care of children in institutions to reflect on what may have happened and whether lessons could be learned to prevent the mistakes of the past being repeated in the future.

"We realise that this may be a challenging process for everyone involved but it is our hope that everybody, whether from Government or from the institutions, who is requested to assist the inquiry will cooperate with the inquiry in a frank, open and whole-hearted way so that this unique opportunity will not be wasted," he added.

The inquiry will begin taking evidence later this month about alleged abuse at homes run by the Sisters of Nazareth nuns in Londonderry, Nazareth House Children's Home in Bishop Street and St Joseph's Home in Termonbacca.

It will consider abuse at Rubane House run in Kircubbin, Co Down, by the De La Salle Brothers order and will later look at the plight of 61 children allegedly abused before they were sent to Australia.

They were known as child migrants, transported during the 1940s and 50s and in some cases abused further after they arrived.

The fourth section of the inquiry will look at Nazareth House in Belfast, where convicted paedophile priest Fr Brendan Smyth's role will be examined.

Later sessions will consider abuse at Kincora and at Barnardo's homes near the city.

Ms Smith said some institutions have made admissions, but the inquiry will focus on areas where the evidence is disputed.

She expected that criminal proceedings would follow in some cases; where there is an imminent risk of prosecutions hearings will be held in private, to avoid prejudicing any case.

The inquiry's remit is limited to children's residential institutions in Northern Ireland, meaning alleged clerical sexual abuse outside the confines of homes, those in foster care or in laundries run by a religious order cannot be examined.

Public hearings are due to finish in June 2015 with the inquiry team to report to Stormont's Executive by the start of 2016.